The present invention relates to an x-ray tube, and more particularly, to an x-ray tube wherein a ceramic bulb, a ceramic stem, and an output window are brazed together using a brazing agent.
Japanese Patent Application Publication (Kokai) Nos. HEI-9-180630 and HEI-9-180660 disclose technologies in this field. An x-ray tube 100 disclosed in these publications has as shown in FIG. 10 a sealed vessel 104 configured from a ceramic bulb 101, a ceramic stem 102 fixed to one open end of the ceramic bulb 101 by a brazing agent P, and an output window 103 fixed to another open end of the ceramic bulb 101 by a brazing agent R. Further, a low voltage cathode pin 105 and a high voltage cathode pin 106 are fixed onto the ceramic stem 102. An electron discharge filament 107 is disposed in the sealed vessel 104 so as to span between the cathode pins 105 and 106. Also, a cylindrical focusing electrode 108 is disposed in the sealed vessel 104 so as to surround the filament 107. A lower end portion 108a of the cylindrical focussing electrode 108 is sandwiched between the ceramic bulb 101 and the ceramic stem 102 with interposing the brazing agent P therebetween so that the ceramic stem 102 is fixed with respect to the ceramic bulb 101. In this way, each component is connected together with interposing the brazing agent P, R therebetween so that assembly of the x-ray tube 100 is improved. Also, the cylindrical focussing electrode 108 and the low voltage cathode pin 105 are connected together by a wire 109 because these need to have the same bias. This wire connection is performed by a subsequent soldering.
However, the following problem exist because the conventional x-ray tube is configured in the above-described manner. That is, because the electric connection between the cylindrical focussing electrode 108 and the low voltage cathode pin 105 is performed through the wire 109, the wiring operation for the wire 109 must be performed separately after the x-ray tube is assembled. Moreover, the wire 109 must be handled with a great care because the wire 109 is exposed out from the x-ray tube.
It is an object of the present invention to overcome the above-described problems and to provide an X-ray tube with excellent assembleability and handling.
To attain the above described object, the present invention provides an x-ray tube including a sealed vessel comprising a bulb having one open end and another open end, a stem fixed to the one open end of the bulb, and an output window fixed to the another open end of the bulb, a low voltage cathode pin and high voltage cathode pin extending through the stem, a filament for emitting electrons spanning between the low voltage cathode and the high voltage cathode in the sealed vessel, a focussing electrode disposed in the sealed vessel and surrounding the filament for converging electrons emitted from the filament and directing the electrons toward the output window so as to discharge an x-ray outwardly out of the output window, characterized by the focussing electrode having a lower end portion sandwiched between the bulb and the stem, and the stem having a surface formed with a metallized layer made from an electrically conductive material, the metallized layer extending at least from the lower end portion of the focussing electrode to the low voltage cathode pin, a brazing material being interposed between the metallized layer and the lower end portion of the focussing electrode for electrically connecting the focussing electrode to the low voltage cathode pin.
The X-ray tube of the present invention is provided with the electrically conductive metallized layer on the surface of the stem. Therefore, during production of the x-ray tube, thermally fusing nature of the brazing agent provided between the stem and the lower end portion of the focussing electrode is improved by the metallized layer. Moreover, the metallized layer extends from the lower end portion of the focussing electrode to the low voltage cathode pin. Therefore, electrical continuity of the focussing electrode and the low voltage cathode is realized on the surface of the stem. Thus, there is no need to perform any separate wiring operations after x-ray tube is assembled. The connection between the focussing electrode and the cathode pin is completed simultaneously with completion of x-ray brazing. Accordingly, assembleability and the handleablity of the X-ray tube can be improved.
Here, the electrically conductive metallized layer is preferably formed on an entire front surface of the stem except an area surrounding the high voltage cathode pin, the front surface of the stem being in confrontation with the output window. Further, in a preferred fashion, a separation groove surrounding the high voltage cathode pin is formed. The electrically conductive metallized layer is removed at a position of the separation groove.
When this type of configuration is used, the metallized layer can be formed at one time over the entire surface of the stem. Therefore, the formation of the metallized layer that is to bring the lower portion of the focussing electrode and the low voltage cathode pin into the electric continuity can be efficiently and simply performed. Also, by forming the separation groove around the high voltage cathode pin, electrical insulation between the high voltage cathode pin and the low voltage cathode pin can be accomplished in the stem surface. Moreover, because the high voltage cathode pin is disposed at an inner side of the separation groove, even if the molten brazing agent flows on the metallized layer, any excessive brazing agent can flow into the separation groove. Thus, assembleability and high yieldability of the x-ray tube using brazing agent can be assured.
In another embodiment, the electrically conductive metallized layer is formed on the stem surface in confrontation with the output window, and the metallized layer includes a first metallized layer having a ring shape matching a contour of the lower end portion of the focussing electrode, and a second metallized layer having a linear shape and radially inwardly extending from an inner periphery of the first metallized layer to the low voltage cathode pin.
In still another embodiment, the electrically conductive metallized layer has a U-shaped configuration having a front surface portion on a front stem surface which is in confrontation with the output window, and a rear surface portion continuous with the front surface portion and at a position on a rear stem surface opposite to the front stem surface. The front surface portion of the metallized layer is formed at a position in contact with at least a part of the lower end portion of the focussing electrode, and the rear surface portion of the metallized layer is formed to reach the low voltage cathode pin.